The objective of this project is to define the initial, intra-cellular events of steroid hormone action. Synthetic glucocorticoid derivatives, some of which could react to form covalently labelled receptors via affinity labelling, are being used with glucocorticoid-responsive rat hepatoma tissue culture cells to examine: (1) steroid-receptor binding site interactions; (2) the effects of steroid binding on receptor conformation; (3) the nature of "activation" of receptor-steroid complexes. A novel group of potential affinity labelling steroids, which may yield a functionally active, covalently labelled receptor, appear promising. Fluorescence spectroscopy represents another technique for examining these interactions. We have developed a new affinity labelling technique called fluorescent chemo-affinity labelling (FCAL) which potentially could give covalent, fluorescent receptor-steroid complexes. Finally we have determined that a class of anti-inflammatory steroids, predicted to be inactive glucocorticoids, are among the most potent glucocorticoids yet described.